According to the birthday paradox, in a group of 23 (or more) randomly chosen people, the probability is more than 50% that some pair of them will have the same birthday. A related coincidence is that 365 times the natural logarithm of 2, approximately 252.999, is very close to the number of pairs of 23 items, 253.
In base 10, 23 is the second Smarandache–Wellin prime, as it is the concatenation of the base 10 representations of the first two primes (2 and 3) and is itself also prime. It is also a happy number in base 10. 23! is 23 digits long in base 10. There are only three other numbers that have this property: 1, 22, and 24.
23 is the smallest prime number p such that the largest consecutive pair of p-smooth numbers is the same as the largest consecutive pair of (p-1)-smooth numbers, as given in the On-Line Encyclopedia of Integer Sequences sequence A228611. That is, the largest consecutive pair of 23-smooth numbers, (11859210,11859211), is the same as the largest consecutive pair of 22-smooth numbers, and 23 is the smallest prime for which this is true.
Nobel Prize-winning economist John Forbes Nash, the inspiration for the film A Beautiful Mind, was obsessed with the number 23 and it featured prominently in his nervous breakdown. He claimed that Pope John XXIII was in fact himself, the evidence being that 23 was his favourite number. Nash also published only 23 scientific articles.
23 is the width of the Arecibo message, sent to space in search for extraterrestrial intelligence.
23 is the TCP/IP port used for telnet and is the default for the telnet command.
Psalm 23, also known as the Shepherd Psalm, is possibly the most quoted and best known Psalm. Psalms is also the 23rd book in the Douay–Rheims Bible.
In Islam, the Qur'an was revealed in a total of 23 years to Muhammad.
Muslims believe the first verses of the Qur'an were revealed to the Islamic prophet Muhammad, on the 23rd night of the 9th Islamic month.
In Abhidharma, the number of anomalous generic types (of a possible 72) - e.g., events are considered sui generis because they are not reducible to either mind or matter — is 23.
The Ancient Chinese believed that numbers conveyed sexuality with even numbers representing femininity and odd representing masculinity. Prime numbers were considered the most masculine and special status was conferred on 23 as it contained not only two consecutive prime numbers (2 and 3) but also the only even prime number.
In popular culture
The number 23 has been retired by a number of professional teams.
Belgian team Club Brugge KV did the same when their number 23, François Sterchele, died in a car accident on May 8, 2008.
In darts, 23 is the lowest score that cannot be gained with the throw of a single dart.
In Hurling, 23 worn by Rory Bolger for Sallins Jnr Hurling as it was the only jersey that would fit.
Alfred Harth uses the number 23 in his artist name Alfred 23 Harth, or A23H, since the year 1+9+8+5 = 23.
British underground electronic label Bad Sekta was officially launched on 23 November 2005. The label and its artists often use the number in their work, regularly releasing music for free on the 23rd day of the month. Bad Sekta's publishing imprint Fear Control was originally known as Twenty Third Publishing.
Several songs and albums use the number 23 as their titles, including Tristan Prettyman's debut album, the eleventh song from Tool's fourth full-length studio album 10,000 Days, "Viginti Tres" (Latin for twenty-three).
Noah23 has several albums which reference the number 23.
Luna's song "23 Minutes in Brussels" (featuring Tom Verlaine) appears on their album "Penthouse".
The composer Alban Berg had a particular interest in the number 23, using it to structure several works. Various suggestions have been made as to the reason for this interest: that he took it from the Biorhythms theory of Wilhelm Fliess, in which a 23 day cycle is considered significant, or because he first suffered an asthma attack on 23rd of the month.[importance?]
In The Matrix Reloaded, the Architect tells Neo it is of utmost importance to choose 23 people to repopulate Zion.
In Jeepers Creepers, the Creeper appears every 23 years for 23 days to feast on human flesh.
In the film Vantage Point, all flashbacks take place 23 minutes before the assassination attempt on the president.
As revealed in Japanese film L: Change the World, 23 is the maximum number of days a person may live before he dies by the cause of writing his name in Death Note. Main protagonist L of the film L: Change the World, signs his name in Death Note so to die after 23 days.
The 23, in South Africa, refers to the 23 conscientious objectors who publicly refused to do military service in the Apartheid army in 1987. The following years the number increased to 143 (in 1988) and 771 (in 1989), with Apartheid being dismantled from 1990 onwards.
^H. Wramsby, K. Fredga, P. Liedholm, "Chromosome analysis of human oocytes recovered from preovulatory follicles in stimulated cycles" New England Journal of Medicine316 3 (1987): 121 - 124
^Barbara J. Trask, "Human genetics and disease: Human cytogenetics: 46 chromosomes, 46 years and counting" Nature Reviews Genetics3 (2002): 769. "Human cytogenetics was born in 1956 with the fundamental, but empowering, discovery that normal human cells contain 46 chromosomes."
^Miriam Dunson, A Very Present Help: Psalm Studies for Older Adults. New York: Geneva Press (1999): 91. "Psalm 23 is perhaps the most familiar, the most loved, the most memorized, and the most quoted of all the psalms."
^Living Religions: An Encyclopaedia of the World's Faiths, Mary Pat Fisher, 1997, page 338, I.B. Tauris Publishers,